Documentation: start documenting driver design patterns

[deliverable/linux.git] / fs / sysfs / file.c

/*
 * fs/sysfs/file.c - sysfs regular (text) file implementation
 *
 * Copyright (c) 2001-3 Patrick Mochel
 * Copyright (c) 2007 SUSE Linux Products GmbH
 * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
 *
 * This file is released under the GPLv2.
 *
 * Please see Documentation/filesystems/sysfs.txt for more information.
 */

#include <linux/module.h>
#include <linux/kobject.h>
#include <linux/kallsyms.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/mutex.h>
#include <linux/seq_file.h>

#include "sysfs.h"
#include "../kernfs/kernfs-internal.h"

/*
 * Determine ktype->sysfs_ops for the given sysfs_dirent.  This function
 * must be called while holding an active reference.
 */
static const struct sysfs_ops *sysfs_file_ops(struct sysfs_dirent *sd)
{
	struct kobject *kobj = sd->s_parent->priv;

	if (sd->s_flags & SYSFS_FLAG_LOCKDEP)
		lockdep_assert_held(sd);
	return kobj->ktype ? kobj->ktype->sysfs_ops : NULL;
}

/*
 * Reads on sysfs are handled through seq_file, which takes care of hairy
 * details like buffering and seeking.  The following function pipes
 * sysfs_ops->show() result through seq_file.
 */
static int sysfs_kf_seq_show(struct seq_file *sf, void *v)
{
	struct sysfs_open_file *of = sf->private;
	struct kobject *kobj = of->sd->s_parent->priv;
	const struct sysfs_ops *ops = sysfs_file_ops(of->sd);
	ssize_t count;
	char *buf;

	/* acquire buffer and ensure that it's >= PAGE_SIZE */
	count = seq_get_buf(sf, &buf);
	if (count < PAGE_SIZE) {
		seq_commit(sf, -1);
		return 0;
	}

	/*
	 * Invoke show().  Control may reach here via seq file lseek even
	 * if @ops->show() isn't implemented.
	 */
	if (ops->show) {
		count = ops->show(kobj, of->sd->priv, buf);
		if (count < 0)
			return count;
	}

	/*
	 * The code works fine with PAGE_SIZE return but it's likely to
	 * indicate truncated result or overflow in normal use cases.
	 */
	if (count >= (ssize_t)PAGE_SIZE) {
		print_symbol("fill_read_buffer: %s returned bad count\n",
			(unsigned long)ops->show);
		/* Try to struggle along */
		count = PAGE_SIZE - 1;
	}
	seq_commit(sf, count);
	return 0;
}

static ssize_t sysfs_kf_bin_read(struct sysfs_open_file *of, char *buf,
				 size_t count, loff_t pos)
{
	struct bin_attribute *battr = of->sd->priv;
	struct kobject *kobj = of->sd->s_parent->priv;
	loff_t size = file_inode(of->file)->i_size;

	if (!count)
		return 0;

	if (size) {
		if (pos > size)
			return 0;
		if (pos + count > size)
			count = size - pos;
	}

	if (!battr->read)
		return -EIO;

	return battr->read(of->file, kobj, battr, buf, pos, count);
}

/* kernfs write callback for regular sysfs files */
static ssize_t sysfs_kf_write(struct sysfs_open_file *of, char *buf,
			      size_t count, loff_t pos)
{
	const struct sysfs_ops *ops = sysfs_file_ops(of->sd);
	struct kobject *kobj = of->sd->s_parent->priv;

	if (!count)
		return 0;

	return ops->store(kobj, of->sd->priv, buf, count);
}

/* kernfs write callback for bin sysfs files */
static ssize_t sysfs_kf_bin_write(struct sysfs_open_file *of, char *buf,
				  size_t count, loff_t pos)
{
	struct bin_attribute *battr = of->sd->priv;
	struct kobject *kobj = of->sd->s_parent->priv;
	loff_t size = file_inode(of->file)->i_size;

	if (size) {
		if (size <= pos)
			return 0;
		count = min_t(ssize_t, count, size - pos);
	}
	if (!count)
		return 0;

	if (!battr->write)
		return -EIO;

	return battr->write(of->file, kobj, battr, buf, pos, count);
}

static int sysfs_kf_bin_mmap(struct sysfs_open_file *of,
			     struct vm_area_struct *vma)
{
	struct bin_attribute *battr = of->sd->priv;
	struct kobject *kobj = of->sd->s_parent->priv;

	return battr->mmap(of->file, kobj, battr, vma);
}

void sysfs_notify(struct kobject *k, const char *dir, const char *attr)
{
	struct sysfs_dirent *sd = k->sd, *tmp;

	if (sd && dir)
		sd = kernfs_find_and_get(sd, dir);
	else
		kernfs_get(sd);

	if (sd && attr) {
		tmp = kernfs_find_and_get(sd, attr);
		kernfs_put(sd);
		sd = tmp;
	}

	if (sd) {
		kernfs_notify(sd);
		kernfs_put(sd);
	}
}
EXPORT_SYMBOL_GPL(sysfs_notify);

static const struct kernfs_ops sysfs_file_kfops_empty = {
};

static const struct kernfs_ops sysfs_file_kfops_ro = {
	.seq_show	= sysfs_kf_seq_show,
};

static const struct kernfs_ops sysfs_file_kfops_wo = {
	.write		= sysfs_kf_write,
};

static const struct kernfs_ops sysfs_file_kfops_rw = {
	.seq_show	= sysfs_kf_seq_show,
	.write		= sysfs_kf_write,
};

static const struct kernfs_ops sysfs_bin_kfops_ro = {
	.read		= sysfs_kf_bin_read,
};

static const struct kernfs_ops sysfs_bin_kfops_wo = {
	.write		= sysfs_kf_bin_write,
};

static const struct kernfs_ops sysfs_bin_kfops_rw = {
	.read		= sysfs_kf_bin_read,
	.write		= sysfs_kf_bin_write,
};

static const struct kernfs_ops sysfs_bin_kfops_mmap = {
	.read		= sysfs_kf_bin_read,
	.write		= sysfs_kf_bin_write,
	.mmap		= sysfs_kf_bin_mmap,
};

int sysfs_add_file_mode_ns(struct sysfs_dirent *dir_sd,
			   const struct attribute *attr, bool is_bin,
			   umode_t mode, const void *ns)
{
	struct lock_class_key *key = NULL;
	const struct kernfs_ops *ops;
	struct sysfs_dirent *sd;
	loff_t size;

	if (!is_bin) {
		struct kobject *kobj = dir_sd->priv;
		const struct sysfs_ops *sysfs_ops = kobj->ktype->sysfs_ops;

		/* every kobject with an attribute needs a ktype assigned */
		if (WARN(!sysfs_ops, KERN_ERR
			 "missing sysfs attribute operations for kobject: %s\n",
			 kobject_name(kobj)))
			return -EINVAL;

		if (sysfs_ops->show && sysfs_ops->store)
			ops = &sysfs_file_kfops_rw;
		else if (sysfs_ops->show)
			ops = &sysfs_file_kfops_ro;
		else if (sysfs_ops->store)
			ops = &sysfs_file_kfops_wo;
		else
			ops = &sysfs_file_kfops_empty;

		size = PAGE_SIZE;
	} else {
		struct bin_attribute *battr = (void *)attr;

		if (battr->mmap)
			ops = &sysfs_bin_kfops_mmap;
		else if (battr->read && battr->write)
			ops = &sysfs_bin_kfops_rw;
		else if (battr->read)
			ops = &sysfs_bin_kfops_ro;
		else if (battr->write)
			ops = &sysfs_bin_kfops_wo;
		else
			ops = &sysfs_file_kfops_empty;

		size = battr->size;
	}

#ifdef CONFIG_DEBUG_LOCK_ALLOC
	if (!attr->ignore_lockdep)
		key = attr->key ?: (struct lock_class_key *)&attr->skey;
#endif
	sd = kernfs_create_file_ns_key(dir_sd, attr->name, mode, size,
				       ops, (void *)attr, ns, key);
	if (IS_ERR(sd)) {
		if (PTR_ERR(sd) == -EEXIST)
			sysfs_warn_dup(dir_sd, attr->name);
		return PTR_ERR(sd);
	}
	return 0;
}

int sysfs_add_file(struct sysfs_dirent *dir_sd, const struct attribute *attr,
		   bool is_bin)
{
	return sysfs_add_file_mode_ns(dir_sd, attr, is_bin, attr->mode, NULL);
}

/**
 * sysfs_create_file_ns - create an attribute file for an object with custom ns
 * @kobj: object we're creating for
 * @attr: attribute descriptor
 * @ns: namespace the new file should belong to
 */
int sysfs_create_file_ns(struct kobject *kobj, const struct attribute *attr,
			 const void *ns)
{
	BUG_ON(!kobj || !kobj->sd || !attr);

	return sysfs_add_file_mode_ns(kobj->sd, attr, false, attr->mode, ns);

}
EXPORT_SYMBOL_GPL(sysfs_create_file_ns);

int sysfs_create_files(struct kobject *kobj, const struct attribute **ptr)
{
	int err = 0;
	int i;

	for (i = 0; ptr[i] && !err; i++)
		err = sysfs_create_file(kobj, ptr[i]);
	if (err)
		while (--i >= 0)
			sysfs_remove_file(kobj, ptr[i]);
	return err;
}
EXPORT_SYMBOL_GPL(sysfs_create_files);

/**
 * sysfs_add_file_to_group - add an attribute file to a pre-existing group.
 * @kobj: object we're acting for.
 * @attr: attribute descriptor.
 * @group: group name.
 */
int sysfs_add_file_to_group(struct kobject *kobj,
		const struct attribute *attr, const char *group)
{
	struct sysfs_dirent *dir_sd;
	int error;

	if (group) {
		dir_sd = kernfs_find_and_get(kobj->sd, group);
	} else {
		dir_sd = kobj->sd;
		kernfs_get(dir_sd);
	}

	if (!dir_sd)
		return -ENOENT;

	error = sysfs_add_file(dir_sd, attr, false);
	kernfs_put(dir_sd);

	return error;
}
EXPORT_SYMBOL_GPL(sysfs_add_file_to_group);

/**
 * sysfs_chmod_file - update the modified mode value on an object attribute.
 * @kobj: object we're acting for.
 * @attr: attribute descriptor.
 * @mode: file permissions.
 *
 */
int sysfs_chmod_file(struct kobject *kobj, const struct attribute *attr,
		     umode_t mode)
{
	struct sysfs_dirent *sd;
	struct iattr newattrs;
	int rc;

	sd = kernfs_find_and_get(kobj->sd, attr->name);
	if (!sd)
		return -ENOENT;

	newattrs.ia_mode = (mode & S_IALLUGO) | (sd->s_mode & ~S_IALLUGO);
	newattrs.ia_valid = ATTR_MODE;

	rc = kernfs_setattr(sd, &newattrs);

	kernfs_put(sd);
	return rc;
}
EXPORT_SYMBOL_GPL(sysfs_chmod_file);

/**
 * sysfs_remove_file_ns - remove an object attribute with a custom ns tag
 * @kobj: object we're acting for
 * @attr: attribute descriptor
 * @ns: namespace tag of the file to remove
 *
 * Hash the attribute name and namespace tag and kill the victim.
 */
void sysfs_remove_file_ns(struct kobject *kobj, const struct attribute *attr,
			  const void *ns)
{
	struct sysfs_dirent *dir_sd = kobj->sd;

	kernfs_remove_by_name_ns(dir_sd, attr->name, ns);
}
EXPORT_SYMBOL_GPL(sysfs_remove_file_ns);

void sysfs_remove_files(struct kobject *kobj, const struct attribute **ptr)
{
	int i;
	for (i = 0; ptr[i]; i++)
		sysfs_remove_file(kobj, ptr[i]);
}
EXPORT_SYMBOL_GPL(sysfs_remove_files);

/**
 * sysfs_remove_file_from_group - remove an attribute file from a group.
 * @kobj: object we're acting for.
 * @attr: attribute descriptor.
 * @group: group name.
 */
void sysfs_remove_file_from_group(struct kobject *kobj,
		const struct attribute *attr, const char *group)
{
	struct sysfs_dirent *dir_sd;

	if (group) {
		dir_sd = kernfs_find_and_get(kobj->sd, group);
	} else {
		dir_sd = kobj->sd;
		kernfs_get(dir_sd);
	}

	if (dir_sd) {
		kernfs_remove_by_name(dir_sd, attr->name);
		kernfs_put(dir_sd);
	}
}
EXPORT_SYMBOL_GPL(sysfs_remove_file_from_group);

/**
 *	sysfs_create_bin_file - create binary file for object.
 *	@kobj:	object.
 *	@attr:	attribute descriptor.
 */
int sysfs_create_bin_file(struct kobject *kobj,
			  const struct bin_attribute *attr)
{
	BUG_ON(!kobj || !kobj->sd || !attr);

	return sysfs_add_file(kobj->sd, &attr->attr, true);
}
EXPORT_SYMBOL_GPL(sysfs_create_bin_file);

/**
 *	sysfs_remove_bin_file - remove binary file for object.
 *	@kobj:	object.
 *	@attr:	attribute descriptor.
 */
void sysfs_remove_bin_file(struct kobject *kobj,
			   const struct bin_attribute *attr)
{
	kernfs_remove_by_name(kobj->sd, attr->attr.name);
}
EXPORT_SYMBOL_GPL(sysfs_remove_bin_file);

struct sysfs_schedule_callback_struct {
	struct list_head	workq_list;
	struct kobject		*kobj;
	void			(*func)(void *);
	void			*data;
	struct module		*owner;
	struct work_struct	work;
};

static struct workqueue_struct *sysfs_workqueue;
static DEFINE_MUTEX(sysfs_workq_mutex);
static LIST_HEAD(sysfs_workq);
static void sysfs_schedule_callback_work(struct work_struct *work)
{
	struct sysfs_schedule_callback_struct *ss = container_of(work,
			struct sysfs_schedule_callback_struct, work);

	(ss->func)(ss->data);
	kobject_put(ss->kobj);
	module_put(ss->owner);
	mutex_lock(&sysfs_workq_mutex);
	list_del(&ss->workq_list);
	mutex_unlock(&sysfs_workq_mutex);
	kfree(ss);
}

/**
 * sysfs_schedule_callback - helper to schedule a callback for a kobject
 * @kobj: object we're acting for.
 * @func: callback function to invoke later.
 * @data: argument to pass to @func.
 * @owner: module owning the callback code
 *
 * sysfs attribute methods must not unregister themselves or their parent
 * kobject (which would amount to the same thing).  Attempts to do so will
 * deadlock, since unregistration is mutually exclusive with driver
 * callbacks.
 *
 * Instead methods can call this routine, which will attempt to allocate
 * and schedule a workqueue request to call back @func with @data as its
 * argument in the workqueue's process context.  @kobj will be pinned
 * until @func returns.
 *
 * Returns 0 if the request was submitted, -ENOMEM if storage could not
 * be allocated, -ENODEV if a reference to @owner isn't available,
 * -EAGAIN if a callback has already been scheduled for @kobj.
 */
int sysfs_schedule_callback(struct kobject *kobj, void (*func)(void *),
		void *data, struct module *owner)
{
	struct sysfs_schedule_callback_struct *ss, *tmp;

	if (!try_module_get(owner))
		return -ENODEV;

	mutex_lock(&sysfs_workq_mutex);
	list_for_each_entry_safe(ss, tmp, &sysfs_workq, workq_list)
		if (ss->kobj == kobj) {
			module_put(owner);
			mutex_unlock(&sysfs_workq_mutex);
			return -EAGAIN;
		}
	mutex_unlock(&sysfs_workq_mutex);

	if (sysfs_workqueue == NULL) {
		sysfs_workqueue = create_singlethread_workqueue("sysfsd");
		if (sysfs_workqueue == NULL) {
			module_put(owner);
			return -ENOMEM;
		}
	}

	ss = kmalloc(sizeof(*ss), GFP_KERNEL);
	if (!ss) {
		module_put(owner);
		return -ENOMEM;
	}
	kobject_get(kobj);
	ss->kobj = kobj;
	ss->func = func;
	ss->data = data;
	ss->owner = owner;
	INIT_WORK(&ss->work, sysfs_schedule_callback_work);
	INIT_LIST_HEAD(&ss->workq_list);
	mutex_lock(&sysfs_workq_mutex);
	list_add_tail(&ss->workq_list, &sysfs_workq);
	mutex_unlock(&sysfs_workq_mutex);
	queue_work(sysfs_workqueue, &ss->work);
	return 0;
}
EXPORT_SYMBOL_GPL(sysfs_schedule_callback);